Fig 1.
Experimental setups for monitoring both locomotor and behavioral activities.
(A): Modified locomotor activity monitors (TriKinetics). Activity of single individuals was recorded in isolation from the social context via crossings of infrared light beams in the center of the glass tubes (B). Ad libitum supply of 5% (w/w) sugar water was provided through sponges (a), separated from the glass tube by plastic nets (b) to allow fluid intake while avoiding chewing by the ant. A metal mesh tunnel segment (c) connected the glass tubes with the feeding devices to provide aeration. Glass tubes were fixed to the monitors by o-rings (d). (C) Experimental setup for the determination of caste affiliation (experiment 1) and for the analysis of daily activities in the social context (experiment 2). Subcolony of individually marked workers of C. rufipes in transparent setup with enclosed brood chamber (left) and open foraging arena with feeding platform (right). (D): forager on the feeding platform. (E): nurses at the brood pile.
Table 1.
Activities displayed by single workers in the foraging arena (foragers) and in the brood chamber (nurses), monitored and continuously quantified over 24 h using time-lapse videos.
Antennating: antennating objects, brood or conspecifics whilst standing. Walking: locomotor movement. Allo(grooming): self-grooming or grooming of conspecifics. Waste management: manipulating or carrying waste material (e.g. food remains, corpses). Trophallaxis: exchange of liquid food between workers. Food consumption: intake of food (foragers: ingestion of sugar water, water and feeding on Drosophila flies in the foraging arena; nurses: feeding on Drosophila flies in the brood chamber). Food transport: carrying Drosophila. Brood relocation: picking up and transporting larvae between the mandibles. Brood care: feeding liquid food to larvae or licking larvae.
Table 2.
Survival rate, proportion of rhythmic individuals and activity characteristics of foragers and nurses isolated in locomotor activity monitors.
Different letters show significant differences between castes within the three light regimes (significance level α = 0.05). Differences in survival and rhythmicity rates were evaluated via χ2 tests; differences in activity periods (τ), total activity levels and proportion of night activity were evaluated via Mann-Whitney-U tests.
Fig 2.
Locomotor activity rhythms of foragers and nurses in isolation from the social context.
Top: Examples of actograms of single workers of each caste. Locomotor activity (indicated as black bars) is shown as double plot under a 12:12h LD-cycle (day 1–8), after a 6 hour phase delay of the LD-cycle (day 9–15) and constant darkness (day 16–22). (A): Actograms of one rhythmic (left) and one arrhythmic (right) forager; (B): Actograms of one rhythmic (left) and one arrhythmic (right) nurse. Bottom: Average activity (mean: solid lines; mean±SE: dashed lines) over 7 days under the respective light regime. (C): Foragers under a 12:12h LD-cycle (n = 78): (D): Nurses under a 12:12h LD-cycle (n = 46); (E): Foragers after a 6 hour delay of the LD-cycle (n = 61); (F): Nurses after a 6 hour delay of the LD-cycle (n = 37).
Fig 3.
Daily time budgets for activities displayed in the social context for both foragers and nurses under the three feeding regimes.
(A): foragers (n = 8) under ad libitum feeding; (B): foragers (n = 12) under daytime feeding; (C): foragers (n = 12) under nighttime feeding; (D): nurses (n = 13) under ad libitum feeding; (E): nurses (n = 12) under daytime feeding; (F): nurses (n = 12) under nighttime feeding. Black: proportion of inactivity, light grey: proportion of caste-specific activity, dark grey: proportion of non caste-specific activity.
Fig 4.
Percentage of foragers and nurses displaying either circadian, ultradian or infradian rhythms of caste-specific activities in the social context, under the three feeding regimes.
Black: circadian rhythms (period lengths between 20 and 28h). Grey: ultradian rhythms (period lengths <20h). White: infradian rhythms (period lengths >28h) (A): foragers (n = 8) under ad libitum feeding; (B): foragers (n = 12) under daytime feeding; (C): foragers (n = 12) under nighttime feeding; (D): nurses (n = 13) under ad libitum feeding; (E): nurses (n = 12) under daytime feeding; (F): nurses (n = 12) under nighttime feeding.
Fig 5.
Examples of caste-specific activity patterns of both foragers and nurses in the social context, under the three feeding regimes.
Activity of single workers is shown for the day phase (yellow area) and night phase (black area) in relation to zeitgeber time (ZT). Feeding times (daytime feeding: ZT 4; nighttime feeding: ZT 16) are indicated as dashed red lines. For both castes and the three feeding regimes, one circadian (left) and one ultradian (right) activity pattern are shown as examples. (A): Forager under ad libitum feeding, τ = 22.3h. (B): Forager under ad libitum feeding, τ = 4.5h. (C): Nurse under ad libitum feeding, τ = 21.3h. (D): Nurse under ad libitum feeding, τ = 2.4h. (E): Forager under daytime feeding, τ = 24.6. (F): Forager under daytime feeding, τ = 13.4h. (G): Nurse under daytime feeding, τ = 24.1h. (H): Nurse under daytime feeding, τ = 3.1h. (I): Forager under nighttime feeding, τ = 22.1. (J): Forager under nighttime feeding, τ = 2.8. (K): Nurse under nighttime feeding, τ = 22.4h. (L): Nurse under nighttime feeding, τ = 3.6h.
Fig 6.
Effect of feeding regime on caste-specific activity patterns in the social context, for both foragers and nurses.
Mean activity (solid lines) and mean±SE (dashed lines) are shown for the day phase (yellow area) and the night phase (black area) in relation to zeitgeber time (ZT). Feeding times (daytime feeding: ZT 4; nighttime feeding: ZT 16) are indicated as dashed red lines; (A): foragers (n = 8) under ad libitum feeding; (B): foragers (n = 12) under daytime feeding; (C): foragers (n = 12) under nighttime feeding; (D): nurses (n = 13) under ad libitum feeding; (E): nurses (n = 12) under daytime feeding; (F): nurses (n = 12) under nighttime feeding.
Fig 7.
Effect of feeding regime on foraging activity in subcolonies.
(A): Foraging activity in the course of 24 hours (mean±SE) for each feeding regime (grey: ad libitum feeding, n = 6 subcolonies; white: daytime feeding, n = 15 subcolonies; black: nighttime feeding, n = 12 subcolonies). (B): Foraging activity plotted separately for both the light and dark phases. Boxplots show medians (center lines) and interquartile ranges (boxes) for the three feeding regimes (grey: ad libitum feeding, n = 6 subcolonies; white: daytime feeding, n = 15 subcolonies; black: nighttime feeding, n = 12 subcolonies). Whiskers indicate the minimum and maximum values and open circles show outliers. Different capital letters show differences during the day phase and small letters show significant differences during the night phase between the feeding regimes (Kruskal-Wallis tests with Bonferroni correction, α = 0.017). Asterisks indicate differences between light phase and dark phase within every feeding regime (Wilcoxon signed-rank test with Bonferroni correction, α = 0.017). **: p<0.003; ***: p<0.0003; ns: p>0.017.
Table 3.
Effect of feeding regime on rates of survival and rhythmic daily activity of isolated individuals of both castes in locomotor activity monitors.
Fig 8.
Examples of actograms of workers in isolation from the social context.
Locomotor activity (indicated as black bars) is shown as double plot for single workers of the nurse and forager caste under a 12:12h LD-cycle. For the three feeding regimes, actograms of one rhythmic (left) and of one arrhythmic individual (right) are shown. (A): forager after ad libitum feeding of the subcolony; (B): forager after daytime feeding of the subcolony; (C): forager after nighttime feeding of the subcolony; (D): nurse after ad libitum feeding of the subcolony; (E): nurse after daytime feeding of the subcolony; (F): nurse after nighttime feeding of the subcolony.